The regulation of enzyme levels in rat tissues during normal and abnormal development is the broad subject of this research. Cerebral, biochemical differentiation, with special reference to the enzyme composition of mitochondria and synaptosomes, in rats with experimental phenylketonuria will be compared with that in normal rats. Research on cancer will be concerned mainly with the systemic effect of neoplasms, with alterations in enzyme levels in the plasma and liver of rats carrying various transplanted neoplasms. BIBLIOGRAPHIC REFERENCES: Greengard, O.: Steroids and the maturation of rat tissues. Journal of Steroid Biochemistry, 1975. Vol. 5. Greengard, O.: Cortisol Treatment of neonatal rats: Effects on enzyme in kidney, liver and heart. Biol. Neonate 27:352-360, 1975.